well you can buy a better battery (AGM) for more $$$ (say 300+) but it doesn't solve the problem and killing an expensive battery will not improve your day

You know if that meter your friend put in (and I am assuming it is a meter not a gage) is powered up all the time not just when the key is in ACC...

 

I'm not sure if it is powered up all the time. I did however ask him if the tach could be the cause of my battery draining when it started happening. He told me it wouldn't. I trusted his word because he was a mechanic at the time. But it wouldn't surprise me if it is. I'm not mechanically inclined, so that's why I had him install it. But I swear the drain started to happen after it was installed.

Here is the tach I had installed